Microstrip four-port circulator using a ferrite coupled line section

This paper describes an alternative configuration of a four-port circulator realized in a microstrip ferrite coupled line technology. The proposed fully planar device employs two three-port circulators consisting of a ferrite coupled line junction and T junction. Both circulators are connected through the same arm, hence, the problem of anti-parallel magnetization met in this type of circulators is avoided without the increase of the device width. The simulated and experimental results check feasibility of such device. The constructed four-port ferrite coupled line circulator is applied as a double isolator operating in the frequency band from 9 to 18 GHz, with average insertion losses -3dB and isolation better than -20dB.